Optical and microphysical properties of natural mineral dust and anthropogenic soil dust near dust source regions over northwestern China

Abstract

Mineral dust aerosols (MDs) not only influence the climate by scattering and absorbing solar radiation but also modify cloud properties and change the ecosystem. From 3 April to 16 May 2014, a ground-based mobile laboratory was deployed to measure the optical and microphysical properties of MDs near dust source regions in Wuwei, Zhangye, and Dunhuang (in chronological order) along the Hexi Corridor over northwestern China. Throughout this dust campaign, the hourly averaged (±standard deviation) aerosol scattering coefficients ( σ sp, 550ĝ€nm) of the particulates with aerodynamic diameters less than 2.5ĝ€μm (PM2.5) at these three sites were sequentially 101.5ĝ€±ĝ€36.8, 182.2ĝ€±ĝ€433.1, and 54.0ĝ€±ĝ€32.0ĝ€Mmĝ'1. Correspondingly, the absorption coefficients ( σ ap, 637ĝ€nm) were 9.7ĝ€±ĝ€6.1, 6.0ĝ€±ĝ€4.6, and 2.3ĝ€±ĝ€0.9ĝ€Mmĝ'1; single-scattering albedos ( I‰, 637ĝ€nm) were 0.902ĝ€±ĝ€0.025, 0.931ĝ€±ĝ€0.037, and 0.949ĝ€±ĝ€0.020; and scattering Ångström exponents (Åsp, 450-700ĝ€nm) of PM2.5 were 1.28ĝ€±ĝ€0.27, 0.77ĝ€±ĝ€0.51, and 0.52ĝ€±ĝ€0.31. During a severe dust storm in Zhangye (i.e., from 23 to 25 April), the highest values of σ sp2.5 ( ĝ1/4 ĝ€5074ĝ€Mmĝ'1), backscattering coefficient ( σ bsp2.5, ĝ1/4 ĝ€522ĝ€Mmĝ'1), and I‰ 637 ( ĝ1/4 ĝ€0.993) and the lowest values of backscattering fraction ( b 2.5, ĝ1/4 ĝ€0.101) at 550ĝ€nm and Åsp2.5 ( ĝ1/4 ĝ€ĝ'0.046) at 450-700ĝ€nm, with peak values of aerosol number size distribution (appearing at the particle diameter range of 1-3ĝ€μm), exhibited that the atmospheric aerosols were dominated by coarse-mode dust aerosols. It is hypothesized that the relatively higher values of mass scattering efficiency during floating dust episodes in Wuwei and Zhangye are attributed to the anthropogenic soil dust produced by agricultural cultivations.